1. Field of the Invention
This invention generally relates to a multi-layer plastic pipe and a method for manufacturing the same, and, in particular, to such a plastic pipe as a duct for use as an automobile component like an intake manifold.
2. Description of the Prior Art
Since the advent of a method for manufacturing a plastic pipe whose center axis varies two-dimensionally or three-dimensionally in an arbitrary manner by blow molding, many of the pipes or ducts used in automobiles have been and still are being replaced with plastic pipes and ducts. By providing such plastic pipes having a two-dimensional or three-dimensional arbitrary shape, for example, when ducts or pipes are to be disposed in a limited space of an automobile, such as an engine room, without the necessity to assemble a plurality of pipe components having simpler shapes, a plastic pipe of a unitary structure having a complicatedly bent shape, either two-dimensionally or three-dimensionally, can be provided, which contributes to facilitate an mounting operation of ducts or pipes. In addition, with such a plastic pipe of a unitary structure, since there is no connection between pipe components, there is no possibility of occurrence of leaks of a fluid passing through the ducts or pipes. For this reason, many of the conventional ducts or pipes made of rubber or the like for use in an engine room of an automobile have been and are being replaced by plastic pipes.
However, for example, even for duct and pipes for use in an engine room of an automobile, the required conditions may vary radically depending on the conditions in which they are used. In particular, since such a duct or pipe as an intake manifold is directly mounted on an engine, it is exposed to a significantly high temperature, and, moreover, since a vibration is directly applied thereto, a high degree of durability is required. For such a reason, the conventional intake manifold of an automobile was normally fabricated from a metal, such as aluminum. However, when a duct or pipe is to be manufactured from a metal, its manufacturing operation is complicated, difficult and expensive, and, moreover, the shape of a duct or pipe to be manufactured tends to be limited.
Therefore, a considerable effort and a sizable amount of money have been expended to try to replace such a duct or pipe as an intake manifold with a plastic duct or pipe;
however, since it is a kind of duct or pipe which requires a high degree of heat-resistant characteristic as well as an increased durability, there has not yet been proposed any such plastic pipe or duct which can be put to practical use and its manufacturing method.